The Beatles legend's refusal to abide by doctors' orders to stop drinking alcohol after he was diagnosed with a heart murmur in 2005 is said to have caused a rift between him and estranged wife Heather.
An insider told the New York Post newspaper: "This was a major source of problems between him and Heather."
"He has been receiving electrical shocks for two years on his chest to help with his heart and was under strict instructions to stop drinking completely, which he hasn't done."
"It's not a life-threatening condition, but he needs to start taking better care of himself."
It was recently revealed that Paul underwent a top-secret heart procedure at a London hospital in September to open his blocked arteries.
Sources claim he and Heather had a huge argument in April 2006 - shortly before they split - after she postponed a leg operation so he could undergo heart treatment.
The source said: "She focused on him first. He was abusing his body."
A representative for the "Yesterday" singer refused to comment.
Heather, 39 - who lost her left leg below the knee in a motorcycle accident in 1993 - and Paul, 65, have a four-year-old daughter Beatrice.
The couple will begin their divorce battle in the London courts next month.
